You may remember learning that there are three primary colors. That number is very significant
It turns out that to see the different colors we see we have to have different types of receptors to catch light and
that these receptors must be most sensitive to different wavelengths of light
Those who have normal color vision have three different classes of receptors in our cones one specialized for long (red) wavelengths,
one specialized for medium (green) wavelengths, and one specialized for short (blue) wavelengths
This theory is called the trichromatic three color theory. The theory is also called the Young/Helmholtz theory after the scholars who first propsed the theory; Thomas Young and Herman Von Helmholtz
The trichromatic theory explains how we see different colors depending on the strength of the responses from different cones
To see blue, you need to have mostly the short wavelength cone respond - it is similar for green and red
Other colors that are not primaries require a balance of responses across some of the cones
To see yellow you need to have a balance of response from both the middle and long wavelength cones
When all three types of cones respond at a high rate we see white, we see black when none of the cones types are responding much at all
When you mix colored lights as on a computer screen you add different wavelengths together and more wavelengths enter the eye
Notice that white requires a balance of all three primary additive colors
When you mix colored paints or other pigments you subtract wavelengths from the light reflected into the eye because they are absorbed by the object
Fewer wavelengths enter the eye then were present in the original light
if you mix enough different pigments all wavelengths will be absorbed and you will experience black